Hydrogen peroxide is an important intermediate chemical useful in such applications as water treatment, pulp and paper bleaching, and organic synthesis. At present, the commercial process for producing hydrogen peroxide involves anthraquinone autooxidation (see, e.g., U.S. Pat. Nos. 4,428,923 and 6,524,547). The process requires numerous reaction and purification sections, uses a large volume of solvent, and provides a less-than-ideal yield of hydrogen peroxide.
Hydrogen peroxide can also be made by a direct reaction of hydrogen and oxygen in the presence of a suitable catalyst, but so far, low reaction rates, poor selectivities, and potentially explosive reactants have prevented direct H2O2 manufacture from becoming a commercial reality. Considerable interest remains, however, in identifying safe, economic routes.
Known methods of making hydrogen peroxide from hydrogen and oxygen use supported transition metals (Group 3 to 12 elements), especially platinum group metals. A wide variety of inorganic and organic supports have been identified, including activated carbon (U.S. Pat. Nos. 6,168,775 and 6,649,140), fluorinated carbons (U.S. Pat. No. 5,846,898), sulfonic acid-functionalized carbon (U.S. Pat. No. 6,284,213), silica, alumina (U.S. Pat. No. 5,961,948), polymer fiber (U.S. Pat. No. 6,375,920), and ion-exchange resin (U.S. Appl. Pub. Nos. 2003/0215383 and 2004/0151658).
Recently, a technique called “microencapsulation” was used to prepare catalysts with improved properties (see, e.g., Chem. Commun. (2003) 449 and references cited therein; Angew. Chem., Int. Ed. 40 (2001) 3469; J. Am. Chem. Soc. 120 (1998) 2985). EP 0 498 166 A1 discloses an alumina-supported Pd catalyst impregnated with 4-bromostyrene or styrene that is subsequently polymerized (see Example 7 and Comparative Example 8). Only the poly(4-bromostyrene)-coated catalyst is active in generating hydrogen peroxide from hydrogen and oxygen. U.S. Appl. Pub. No. 2004/0184983 describes a catalyst consisting of: (a) one or more metals of the platinum group as active components; (b) one or more polyolefins; and (c) a carrier. The polyolefin is dissolved in a solvent, and the resulting solution is used to impregnate the carrier or the catalyst. The catalyst is useful in producing hydrogen peroxide from hydrogen and oxygen in a reaction solvent containing a halogenated promoter and/or an acid promoter.